Update PlasmaWindowModel test to reflect VirtualDesktop changes

Summary:
Before we send the data we don't know what desktop a client is on.

It used to be neither on all desktops nor on any desktop, a corrupt
state.

After the virtual desktop changes the data will will indicate that we're
on all desktops until we're told otherwise, which is at least a valid
state.

Test Plan: Ran test

Reviewers: KWin, mart

Reviewed By: KWin, mart

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D16880